Dual plug ignition system



March 1952 E. w. LAUTENBERGER DUAL PLUG IGNITION SYSTEM Filed July 6,1950 Inventor Elmer- W. Lautenber i er by M Y His Attorney Patented Mar.23, 1952 DUAL PLUG IGNITION: SYSTEM Elmer W. Lantenberger, Schenectady,N. Y., as.-

si'gnor to General Electric Company, a corpo- Application Julyfi, 1950,Serial No. 172,337

tional ignition systemsv almost invariably fail to light their burnersand, numerous attempts to overcome this res-tart difficulty-haverailed.

Indications have been. that-1a larger spark gap improves altitudestarting performance; However,, there is" a practical limit to which aspark gapcan belengthened'and this depends upon the available outputvoltage of the ignition unit which units already' produce the maximumline to ground voltages that it is practical toimpress on high-tensionignition cables which are: also already stressed well. beyond theircorona level. The lack of a practical ignition system due to theforegoing problem has. heretofore imposed'a serious limitation on thedevelopment and operationof jet engines otherwise capable of highaltitude flying.

It is an object of. this inventionl to provide an ignition system whichovercome the foregoing restart'difliculties at high altitudesand yetwhich is simple andipositive inoperation.

It is-a f'ur-ther object of this invention to provide' an ignitionsystem which is particularly adapted for high altitude jetengineaircraft.

Still. another object of: this invention is top-rovide an ignitionsystem which will operate at both lowand high altitudeswhileoat the sametime providing thetype of electrical discharge required at. the higheraltitudes to initiate combustion.

A still further objectof myinventionis toprovide an ignition. system.in. which two separate spark plugs are. used in the same combustionchamber, neither of which plugs have a ground electrode.

Astill further, object of this invention is topro vide an ignitionsystem. whlchwill not stress the system insulation beyond presentmaximum practical levels and yet will. provide twice the usuallyavailable voltage to jump the. spark gap.

A still further object of this invention isto provide a system capable.of firing a. spark gap roughly twice as large as the maximum gap thatit is practical to fire with a conventional system.

Still another object is to provide an. electrical discharge forinitiating combustion which has greatly increasedcapacitive andinductive components and consequently provides greater power and energy.

According to my invention, I provide an ignition system which comprisestwo separate spark plugs, each of which plugs are oppositely disposed inthe same combustion chamber and have a single ungroundedelectrode.Ahightension circuit is connected between the two. electrodes and thelatter are energized simultaneously, the polarity of the voltageimpulses. on one. electrode being positive andthepolarity of. thevoltage impulses on the other electrode. being. negative '50 that theelectrical discharges. take place in a wide gap betweenlthe twosparkplugs.

The invention will be more. fully understood by referring now. to theaccompanying. drawing of. a diagrammatic representation ofmy improvedignition system as applied to one of, the combustion chambers. of a. jetengine.

The drawing show-ea cross-sectional view of a combustion. chamber Iwhich has an inner liner 2. This chamber represents. one of a pluralityof combustion chambersrwhich are normally annularly disposed within theouter. periphery. of a conventional jet engine.

Projecting into the combustion chamber are two spark plugs 3 and 4which. are of identical construction. Looking at spark plug 3 it, willbe seen. to comprise an elongated high voltage electrode 5 which is.centrally disposedlin a ceramic insulator 5 within a metal housing Ihaving a mounting flange 8 whereby the spark plug 3 may be keyed andsecured to the combustionchambcr. It will be noted that my spark plughas a single extended high voltage electrode. but no ground electrode:.The upper portion above the mounting flange may be of any suitableconventional construction.

As mentioned above, sparkplug. 4 is similar in construction to sparkplug, 3. and they. should be cooperatively located so that the innerextremities of their central-1y disposed. electrodesextend toward eachother irrespective of the. axial disposition of their housing 1. in. thechamber.

Spark plugs 3 and 4. are energized by ignition coils ill and H. Coil ithas a primary or.low tension winding l2 and, a secondary or high tensionwinding I 53 and one end of each of these windings are connectedtogethenthe opposite end of high tension winding 13 being connected by acable 14. to the. single electrode 5 of spark plug 3.

Ignition coil H is similar to. the one just. described, it alsocomprising a low tension winding l5 and a high tension winding Hi,having, one end 3, of each connected together, the other end of the hightension winding l6 being connected via cable H to the single electrode 9of spark plug 4. The two high tension windings l3 and iii are seriallyconnected together at IS.

A source of sparking voltage for my system may be obtained in a numberof different ways known to the art. For purposes of illustrating acompletely operative system, I have shown a vibrator type batteryoperated system which uses a conventional electrical circuit except thatan additional ignition coil, and a capacitor having twice the usualcapacity, have been added to the circuit as will hereinafter bedescribed.

As shown in the drawing, a battery [-9 is connected in series with aswitch 20, ignition coil primaries l2 and I5, and with a circuitcomprising the parallel arrangement of a capacitor 2| and a vibrator 22.The ignition coil primaries have approximately two-thirds the number ofturns normally employed in a conventional single ignition coil circuit.One side of the battery i9 is connected to one end of ignition coilprimary l5 and grounded at 24.

The vibrator 22 is seen to comprise a reed 23 at the top of which ismounted an armature 24. In addition, the reed 23 carries two pairs ofcontacts 25 and 26 which operate with the reed as will be explained.When the reed 23 is at rest, contacts 25 are closed, and a circuit maybe traced through an electromagnet 21 to ground.

With the foregoing understanding of the elements and their organization,the operation of my invention will be readily understood from thefollowing explanation. When the switch is closed, current will flowthrough closed contacts 25, electromagnet 21 and to ground thus causingthe armature 24 to be drawn to the right thereby closing contacts 26.This will cause current to build up in the ignition coil primaries l2and I5. After contact has been established at 25, the contacts at 25will open and the electromagnet 21 will be de-energized and the reed 23will return to the left position. This cycle will continue and currentflow to the ignition coil primaries i2 and [5 will be alternatelyestablished and interrupted. With each interruption, the flux producedby current in the ignition coil primaries, collapses at a very rapidrate. Much of this flux links the ignition coil secondaries l3 and 16 aswell as the primaries l2 and I5. The rapid rate of decay of flux in eachof these ignition coils induces voltages in both the primary andsecondary windings. Because the secondary windings have more than onehundred times as many turns as the primary windings their voltages arecorrespondingly very much higher. As shown in the drawing, the ignitioncoils are connected to produce voltages in coils l3 and I6 which are 180out of phase so that spark plug 3 will be energized by a high voltagehaving a polarity opposite to that of the high voltage supplied to sparkplug 4. This results in developing a voltage which is twice as great asthe voltage developed in a conventional single ignition cell system yetwithoutany increase in the line to ground voltage stress on ignitioncables l4 and IT.

The opening of contacts 26 causes capacitor 2! to be switched into theprimary circuit and this capacitor thereupon becomes charged by thevoltage which was induced in primary coils l2 and I5. Due to thesecondary capacitance of the cables and spark plugs, they also will becharged by the voltage induced in secondary coils l3 and 16. At theinstant that the voltage between electrodes 5 and 9 reaches thebreakdown potential of the gap a high frequency spark will jump the gapand dissipate the energy stored in the secondary capacitance of thesystem. It will be appreciated that the use of a second high tensioncable and spark plug in my system has doubled this capacitance andenergy in the spark compared to that obtainable from a conventionalsingle spark plug system. Following the discharge of secondarycapacitance, the energy of the primary capacitor is dissipated in thespark at a much lower frequency. This capacitive component is alsogreatly increased in my system since it will be recalled that theaddition of a second ignition coil to the circuit permits the use of aprimary capacitor having twice the electrical size. Finally, theinductive component or are which follows the spark is also greatlyincreased inasmuch as it is produced by the inductive energy of twoignition coils rather than one as in conventional systems.

Thus, the system herein described not only provides twice the outputvoltage usually available and thus makes it possible to substantiallydouble the gap length between electrodes without causing any increase inthe electrical stress on the system insulation, but, furthermore, theenergy of each electrical discharge across the gap is greatly increasedby virtue of the larger capacitive and inductive components of the sparkand are. These advantages obtained when using my ignition system havebeen found by wind tunnel test of a full scale jet engine to result ingreatly improved high altitude starting performance.

In Patent 2,447,782 to Welge, there is shown an ignition system directedto the elimination or suppression of radio frequency interference whichresults from their operation in internal combustion engines. The Welgepatent discloses a system in which a single spark plug has twoelectrodes both of which are insulated from ground and fed by a balancedtwo wire system. It will be evident upon examination, however, that thissystem has only a superficial resemblance to my invention since itrequires a close interrelation of leads to the spark plug and this wouldincrease rather than improve the severe corona and insulation breakdownproblems encountered at high altitudes. In my system the cables to theplugs are purposely widely separated which construction is just oppositeto that of the Welge patent which teaches the balancing out of radiointerference voltages. The present invention requires electrodes to bewidely separated and, in fact, to be removed outside the bounds of thesame spark plug in order to provide a greater capacitive component. Itwill be appreciated, therefore, that the above patentees system is notcapable of producing as long and as hot a spark at high altitudes.

It should be understood that my system will operate at sea level as wellas at high altitudes and this will depend partly upon the choice of thegap distance. For practical purposes, and to insure firing at sea levelconditions, I prefer to set the gap between electrodes at about one-halfinch to insure positive starting throughout the altitude range of theaircraft although my system will operate with gap settings severalinches long at altitudes in the order of 50,000 feet provided adequateinsulator flashover distance is built into the exposed end of the sparkplug.

Although a particular embodiment of my invention has been illustratedand described, modifications thereof will readily occur to those skilledin the art. It should be understood, therefore, that the invention isnot limited to the particular arrangement disclosed but that theappended claim is intended to cover all modifications which do notdepart from the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: 7

In an ignition circuit for a jet engine combustion chamber, a pair ofseparate single-electrode spark plugs adapted to project into saidchamber in opposing relation to define a spark gap therebetween, eachsaid plug including means insulating the plug electrode from saidchamber and the external ends of said plug electrodes bein widely spacedapart, a pair of separate ignition transformers each having a lowvoltage primary winding and'iahigh voltage secondary winding, a commonconnection connecting, said primary windings and said secondary windingsrespectively in backtd-back series circuit relation thereby toprovide'at opposite ends of said secondary windings instantaneousvoltages of opposite polarity, means grounding said windings at a pointelectrically adjacent said common connection, and a pair of insulatedhigh-voltage lead wires positioned remotely with respect to .each otherand connecting said opposite ends of said secondary windings to saidplug electrodes respectively, whereby said plug electrodes are suppliedwith voltages of opposite polarity with respect to ground and thevoltage applied across said gap is substantially greater than thelineto-ground voltage at any part of saidcircuit.

ELMER W. LAUTEN'BERGER.

REFERENCES orrEn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 578,266 Rowbotham Mar. 2. 1897604,241 Tuttle May 17, 1898 1,888,692 Powers Nov. 22, 1932 2,115,873Powers May 3, 1938 2,447,782 Welge Aug. 24, 1948 2,470,568 MeCrumm May17, 1949

